Gradient Coils in MRI Technology

Gradient Coils: Types and Function

• Gradient coils are used to deliberately alter the main magnetic field (B0) in MRI.
• There are three sets of gradient coils, each for a different direction (x, y, and z).
• Variations in the magnetic field allow for image slice localization, phase encoding, and frequency encoding.
• Z-axis gradient coils consist of Helmholtz pairs.
• X and Y-axis gradient coils are paired saddle coils.

How Gradient Coils are Produced

• Magnetic field strength is proportional to the current, number of loops, loop size, and spacing of the loops.

• Changing these parameters allows for varying magnetic field strength in a specific direction (increasing or decreasing).

• Gradient strength is measured in units of G/cm or mT/m, signifying the Gauss or milliTesla change over a centimeter or meter.

• Stronger gradients (e.g., 15 or 20 mT/m) lead to higher speed and resolution imaging.

• Gradient coils are wires within the magnet, creating superimposed magnetic fields upon the main magnetic field.

• Three sets of wires (X, Y, and Z) are used, each generating a field in a specific direction.

• Current fed into the Z gradient creates a magnetic field in the Z direction.

• Gradient coils are tightly fixed in resin to create a strong magnetic field.

• Gradient coils provide a linear gradation (slope) of magnetic field strength from one end of the solenoid to the other. This gradient is created by passing current through gradient coils. This increases or decreases the magnetic field on either side of the isocenter.

• The magnetic field generated by gradient coils is very strong, however, coils are fixed in resin to avoid vibrations and noise.

• Three gradient coils form a cylinder, which is then placed within the main magnet bore.

MR Systems and Gradient Coils

• MRI systems use three sets of gradient coils (x, y, and z) to create magnetic field gradients for image formation.
• The positioning of these coils allows for specific image plane creation.

This quiz explores the types and functions of gradient coils used in MRI, detailing their role in altering the main magnetic field for imaging. It also covers the production and measurement of gradient strength, providing insights into how variations enhance image resolution and speed.